Natural-inspired sustainable cellulose cooling aerogel with hetero-photonic scattering network via hydration of metal-organic frameworks-induced interface assembly for energy saving buildings

Passive radiative cooling is a sustainable cooling technology that shows great promise in energy-saving fields. However, simultaneously achieving solar reflectivity and infrared emissivity over 95% performance is hindered by the lack of an efficient micro/nano-structure process technology and by photonic design's shortcomings in terms of high cost and environmental concerns. Herein, inspired by the structural relationship in the white beetle, a novel cooling cellulose aerogel (MCA) with dual-band solar reflectivity and infrared emissivity was proposed by meticulously manipulating the kinetics of the ice-templating process. A hetero-photonic scattering topology composed of nanoparticles, a nano/micro fibres network, and dual-pores via incorporating ice nucleation modifier of hygroscopic metal-organic frameworks (MOF) (modulation of interaction between cellulose, water, and MOF), reproducing the random and anisotropic optical scattering mechanism of white beetles. Driven by the hydration of MOF-induced ice nucleation in binary nanocellulose suspensions, the nanofibers and nanoparticles can form a heterostructured and interconnected micro/nanonetwork via hydrogen bonding and electrostatic interactions. Compared with the traditional pore structure, the bioinspired MCA exhibited a dual band high solar reflectance of 0.958 and infrared emissivity of 0.95, which results in daytime subambient cooling of 7.1 °C during direct sunlight outdoors. Meanwhile, life cycle assessment demonstrates that the preparation process of MCA exhibits a very low environmental impact and is essential for green production and manufacturing. By demonstrating 40% annual cooling energy savings in China, this work paves the way for high-performance, sustainable cooling materials.